Method for the recovery of hydrocarbon vapors



06t- 9, 1956 R. F. HARTMAN ETAL METHOD FOR THE RECOVERY OF HYOROOARBON vAPORs Filed Jan. 3l, 1955 @ATTORNEYS METHOD FR THE RECOVERY F HYDRCRBN VAPRS Robert F. Hartman, El Segundo, Edward H. Lynch, Manhattan Beach, and Laverne I. Elliott, Berkeley, Calif., assignors, by direct and rnesne assignments, to California Research Corporation, San Francisco, Calif., a corporation of Delaware Application January 31, 1955i, Serial No. 484,962

Claims. (Cl. 1S3--115r) This invention yrelates to a method for recovering hydrocarbon vapors from a vessel -containing ai-r and normally liquid hydrocarbons, and, more particularly, to a method for recovering valuable hydrocarbons vaporized from a mixture of normally liquid hydrocarbons as they are loaded into a container.

In the loading of liquid hydrocarbons into tanks, trucks, ships and the like, normal operations are to displace the air contained in these empty vessels with the liquid, allowing the Vair to be vented into the atmosphere. However, even when loading higher boiling hydrocarbon mixtures such as gas oils, a certain amount of vaporization of the low boiling components in the oil occurs, thus resulting in the release of these vapors to the atmosphere along with the a-ir. The ellux of vapor from the vessel increases as the temperature increases and as the boiling range of the liquid mixture decreases, so that when the liquid is gasoline, considerable quantities of C4 and C5 hydrocarbons are discharged through the venting apparatus. With the problem of 'air pollution being one of concern to the petroleum industry as well as the public, it would be highly desirable to prevent the escape of these vapors, thus -reducing the smog conditions existing in many parts of the world. Furthermore, by venting these hydrocarbon vapors into the atmosphere, these valuable hydrocarbons are irretrievably lost.

Accordingly, it -is an object of the present invention to provide a method for recovering substantially all of the hydrocarbons vaporized during `the loading of normally liquid hydrocarbon mixtures into tanks and the like, thus preventing the discharge of such vapors into the Iair as contributors of atmospheric pollution.

-Further objects will be apparent from a consideration `of the description to follow.

According to the present invention, an air-vapor mixture is recovered from a vessel and passed into a saturation zone wherein the mixture is substantially saturated with respect to its hydrocarbon content by cont-acting the mixture with a liquid stream of normally liquid hydrocarbons. The saturated air-vapor mixture is withdrawn from the saturation Zone, compressed to a pressure in the range of from about 50 to 1000 p. s. i. g., and introduced into a contacting Zone such as an absorber, mixer, or the like, wherein the mixture is intimately contacted with a liquid stream of normally liquid hydrocarbons. From the contacting zone are recovered a gaseous phase which is relatively free of hydrocarbon vapors, and the liquid hydrocarbon stream introduced into the contacting zone as enriched with hydrocarbons from the compressed airvapor mixture. lt has been found that the present invention is particularly effective in recovering vaporized components of gasoline, and thus, the liquid hydrocarbon employed in the saturation and contacting zones is preferably a petroleum fraction boiling in the gasoline range.

The invention can be more clearly understood by reference to the appended drawing which is a diagrammatic illustration of a process flow suitable for the practice of 2,765,872 Patented @etu 9, 1956 the present invention. Since the present invention is particularly applicable to gasoline loading operations, the drawing shows one embodiment of the subject invention as `applied to tank truck gasoline loading facilities. No attempt is made -to indicate valves, control equipment, and the like, since the location thereof can readily be supplied by those skilled in the art.

Referring to the drawing, lilling operations are conducted by passing gasoline from storage tank 10 through line 11, ,pump 1-2, and line 13 Iinto tank truck l1d. In passing into the truck, some of the lighter components of the gasoline are vaporized into the yair contained in the vessel. This :air-vapor mixture is collected from the vessel, for example, by means of a collapsible viitting that is inserted in a vent in the vessel which, when expanded, forms a vapor-tight collecting device, and is then passed through flexible hose 15, line 16, ame arrester or lire check 17, and line 1S into saturation pot 19, the latter comprising a saturation Zone.

IIn the saturation pot, the air-Vapor mixture is int-imately contacted with gasoline Ientering the pot from tank 10 through line 11, pump 12, line 13 and line 20. This contacting step serves two purposes, the rst being to saturate the air-vapor in respect to its hydrocarbon content so yas -to prevent the formation of :an explosive mixture, thereby eliminating a potential hazard in the subsequent treatment of the Iair-vapor mixture. The second purpose, which is applicable to a preferred embodiment of the .present invention, is that upon the passage of 'the gasoline into the pot, a certain amount of vaporization of light hydrocarbons contained in the gasoline occurs, the liquid gasoline removed fro-1n the -pot by line 21 thus being depleted of these light ends, thereby improving its absorbing ability `for 4'use in a subsequent treating step. As not-ed before, the gasoline is removed from the pot by line 21, from which it is pumped by pump 22 into line 23, from which latter line it can be returned to storage tank 10 by lines `24 and 36, or, preferably, is passed by line 23 to an absorber hereinafter described.

The saturated air-vapor mixture `is passed from pot 19 by lines 25, 37, and 27 Ito compressor 28, or, more desirably, by line 25 into gas holder 26, -as shown in the drawing. The gas holder is preferably a vessel that takes in fluctuating amounts `of gas but discharges only la constant, controlled amount. A-n example of such a holder is a spherical vessel which has a hemispherical flexible membrane on -the inside, the outer edge of the membrane being fastened to the shell of .the sphere at the equator. The air-vapor mixture is stored between the membrane and the shell.

From the gas holder 26 the air-vapor mixture is passed by line 27 into a compressor 28 wherein the mixture is compressed to a pressure in the range of from about 50 to 1000 p. s. i. g., and preferably in the range of from about 100 to 300 p. s. i. g. In the form shown in the drawing, this is `accomplished by passing the vapor from holder 26 by line 27 into the first-stage 28a of compresser 28, with the partially compressed mixture then being passed through line 29 into interstage cooler 30 (wherein the lmixture is cooled preferably to a temperature below about 275 F. by indirect contact with gasoline, the source of the latter being discussed below). The cooled air-vapor mixture is then passed by line 31 into the second-stage 23h of the compressor from which it is removed at the desired pressure by line `32 and passed into absorber 33, the latter comprising a contacting zone.

In the absorber 33 the mixture is intimately contacted with a normally liquid hydrocarbon, desirably gasoline, or, in a preferred manner, with the light hydrocarbon depleted gasoline from the saturation pot 19 which is passed into the absorber by line 23. This gasoline absorbs over by weight of the hydrocarbons contained in the airhydrocarbon vapor mixtures displaced from the truck 14 through line 16 so that upon removal of the gaseous phase from the absorber by line 34, less than 25% of the hydrocarbon vapors recovered from the truck are lost. The liquid gasoline, now `enriched in light hydrocarbons, is removed from absorber 33 by line 35 and is passed through icooler 30 where it Icools the partially compressed air-vapor mixture from the iirst-stage of the compressor 28 by indirect heat transfer, after which the gasoline is discharged into storage tank 10 by line 36. In this embodiment of the invention, the heat absorbed by the gasoline during the absorbing .and cooling stages is dissipated in storage tank 10 which acts as a heat sink.

As noted and described above, a gas holder 26 is included in the preferred embodiment of the present invention. Since the loading of tanks, trucks, and ships is an intermittent operation, it is apparent that the collection of vapors is also of the same nature and thus, if a gas holder is not employed, the recovery facilities will be constantly starting and stopping to handle the surges of recovered vapors. Such intermittent operation requires somewhat complicated instrumentation and control equipment and the occasional attendance by a trained operator. However, the installation of a gas-holding vessel of the vapor-balloc-n type previously described permits the retention of these intermittent surges while allowing a constant, controlled amount of vapor to be discharged from the vessel to the compressor. Thus, an easily instrumented continuous operation of the recovery facilities is effected. Furthermore, by operating continuously, the lines, compressor, and control apparatus can be reduced in size from that required if intermittent operation is employed.

The operation of the present invention, as applied to the embodiment of the process illustrated in the appended drawing, is shown in the following example.

Example Gasoline, with an initial boiling point of 95 F. and an end point of 410 F., is passed at a rate of 90,000 gallons/hr. into a tank truck 14. From the truck is displaced typical air-hydrocarbon vapor mixture of the following composition:

Component Vol. Per- LbJhr.

cent

Air 65. 100. 0

C3 Hydrocarbons 1, 7 4.0 Ci Hydrocarbons. 17. 54. 0 C5 Hydrocarbons... 10. 5 40. 2 Ca Hydrocarbons 5, 3 23. 6

Total Hydrocarbons. 35. 0 121. S

Component: Vol. percent Air 70.0 C3 Hydrocarbons 1.8 C4 Hydrocarbons 17.2 C5 Hydrocarbons 8.9 Cs+ Hydrocarbons 2.1

In theV absorber, the-mixture is contacted with gasolinel 30 while the gaseous phase is passed by line 34 into the From the above example it can be seen that over (by weight) of the hydrocarbons contained in the airvapor mixture displaced from the tanktruck are recovered and retained in the system, while less than 10% of the. hydrocarbon vapors which would normally be vented to the atmosphere are so released through line 34. Thus, the objects ofA the present invention are realized, in that recovery of valuable hydrocarbons displaced from the truck is substantially complete. Furthermore, the absorbing liquid here employed is the same stock asis supplied to the truck, thus avoiding the stripping operations that would otherwise be necessary if the vapors were absorbed in a-special liquid of a diiering boiling range such as sponge oil or the like.

We claim:

l. A method of recovering light hydrocarbon vapors from, a vessel. containing said vapors in admixture with air, whichcomprises recovering the air-vapor mixture from said vessel; substantially saturating said mixture in respect to its hydrocarbon content by contacting said mixture in a saturation zone with a liquid stream of normally liquid hydrocarbons; compressing the resulting saturated, mixture to a pressure in the range of from about 50 to; 1000 p. s. i. g.; contacting the resulting compressed mixture in a contacting Zone with a liquid stream of normally liquid hydrocarbons; and recovering from said contactingzone an overhead gaseous phase which is rela-` tively free of hydrocarbon vapors and can be vented without appreciable contamination to the atmosphere, and, as bottoms from said contacting zone, the liquid hydrocarbon stream introduced therein as enriched with hydrocarbons from the compressed mixture.

2. The method of claim 1 wherein the substantially saturated mixture iscompressed to a pressure in the range of from about to 300 p. s. i. g.

3. The method of claim 1 wherein the liquid hydrocarbon streams employed are gasolines.

4. A method of recovering light hydrocarbon vapors froma vessel containing said vapors in admixtnre with air, which comprises removing the air-vapor mixture ironrsaid vessel and contacting said mixture in a saturation zone lwith-a liquid stream of gasoline; recovering from said zone an air-vapor.V overhead fraction substantially'saturated With-respect to its hydrocarbon content andra gasoline bottoms fraction; passing said overhead fraction into a gas holder; continuously withdrawing said saturated air-vapor mixture from said gas holder and compressinglthe mixture to a pressure in the range of from about 50 to v1000 p. s. i. g.; passing the resulting compressed mixture into a contacting zone wherein it is contacted with liquid gasoline; and continuously recovering from said contacting zone an overhead vgaseous phase which is relatively free of hydrocarbon vapors and can be vented without'appreciable ycontamination tothe atmosphere, and, as bottoms from said contacting zone, ahydrocarbon-enriched lliquid stream of gasoline.

5. The method of claim 4 wherein at least a portion of the gasoline bottoms fraction recovered from the saturation zone is passed into the contacting zone so as to Contact the compressed air-vapor mixture. Y

6. T he method of vclaim 4. wherein the contacting zone is an absorber.

7. The method of claim 4 wherein the saturated airvapor mixture is compressed to a pressure in the range of from about 1GO to 300 p. s. i. g.

8. In a truck loading station wherein gasoline is intermittently passed from a storage tank into a Vessel upon a truck, the method of avoiding contamination of the atmosphere by the hydrocarbon vapors displaced from said vessel as the same is lled with gasoline, which comprises removing the air-vapor mixture from said vessel and contacting said mixture in a saturation zone with a liquid stream of gasoline; recovering from said zone an air-vapor overhead fraction substantially saturated with respect to its hydrocarbon content, and a gasoline bottoms fraction; passing said overhead fraction into a gas holder; continuously withdrawing said saturated air-vapor mixture from said gas holder and compressing the mixture to a pressure in the range of from about 50 to 1000 p. s. i. g. in a compressor; passing the resulting compressed mixture into an absorber wherein it is contacted with at least a portion of the liquid gasoline bottoms fraction recovered from said saturation zone; and continuously recovering from said absorber an overhead gaseous phase which is relatively free of hydrocarbon vapors and can be vented without appreciable contamination to the atmosphere, and, as bottoms from said absorber, a hydrocarbon-enriched stream of gasoline.

9. The method of claim 8 wherein the saturated airvapor mixture withdrawn from the gas holder is compressed to a pressure in the range of from about 50 to 1000 p. s. i. g. in a multi-stage compressor, said air-vapor mixture being cooled between at least one of the compression stages in at least one interstage cooling zone.

10. The method of claim 9 wherein at least a portion of the hydrocarbon-enriched bottoms stream of gasoline recovered from the absorber is passed into at least one of the interstage cooling Zones so as to cool, by indirect heat exchange, the air-vapor mixture as it passes between the stages of the multi-stage compressor.

References Cited in the le of this patent UNTED STATES PATENTS 2,252,687 Bassett Aug. 19, 1941 2,689,625 Davis Sept. 21, 1954 

1. A METHOD OF RECOVERING LIGHT HYDROCARBON VAPORS FROM A VESSEL CONTAINING SAID VAPORS IN ADMIXTURE WITH AIR, WHICH COMPRISES RECOVERING THE AIR-VAPOR MIXTURE FROM SAID VESSEL; SUBSTANTIALLY SATURATING SAID MIXTURE IN RESPECT TO ITS HYDROCARBON CONTENT BY CONTACTING SAID MIXTURE IN A SATURATION ZONE WITH A LIQUID STREAM OF NORMALLY LIQUID HYDROCARBONS; COMPRESSING THE RESULTING SATURATED MIXTUTE TO A PRESSURE IN THE RANGE OF FROM ABOUT 50 TO 1000 P.S.I.G.; CONTACTING THE RESULTING COMPRESSED MIXTURE IN ACONTACTING ZONE WITH A LIQUID STREAM OF NORMALLY LIQUID HYDROCARBONS; AND RECOVERING FORM SAID CONTACTING ZONE AN OVERHEAD GASEOUSS PHASE WHICH IS RELATIVELY FREE OF HYDROCARBON VAPORS AND CAN BE VENTED WITHOUR APPRECIABLE CONTAMINATION TO THE ATMOSPHERE, AND, AS BOTTOMS FORM SAID CONTACTING ZONE, THE LIQUID HYDROCARBON STREAM INTRODUCED THEREIN AS ENRICHED WITH HYDROCARBONS FROM THE COMPRESSED MIXTURE. 